Answers to Review Questions

Chapter 21 (p. 456)

1. Not every organism that dies becomes a fossil. Many fossils that exist are yet to be discovered. Erosion and other geological events have destroyed fossils. The study of horse fossils has shown that evolutionary change is not constant. Rates vary widely with periods of little change. Even when there is a trend, there are exceptions.

2. In Darwin's day they age-dated rocks by the position of various strata and could only give ages in relation to one another. Now radioactive dating is based on the half-life decay of certain radioisotopes, a definite quantity.

3. Dry summers made food scarce and larger beak size made the difference between survival and starvation.

4. Soot-darkened trees and pollution killed light-colored lichens, so light-colored moths stood out on the dark background and were eaten. Therefore, fewer light-colored moths survived to reproduce and a greater number of dark-colored moths reproduced and passed on their dark-color genes. Industrial melanism refers to the increase of melanin production by organisms to blend into the sootier atmosphere generated by industry.

5. Artificial selection, which we call breeding, demonstrates clearly that selection will produce substantial change in populations. Artificial selection is a good analogy for natural evolution. Artificial selection tends to produce change faster.

6. Homology is the development of seemingly different structures from the same ancestral source (wings in birds and fins on fish). It shows that change has taken place slowly and very demonstrably from earlier forms.

7. Convergent evolution is seen in organisms which are vastly different yet seem to have evolved the same mechanisms to deal with specific environmental pressures (such as albinism and blindness in cave organisms).

8. Darwin showed that an isolated population of organisms rapidly adapted and evolved to fit their habitat, with their closest relative being those encountered in the closest continental region.

9. Scientific creationism is not truly scientific because it is based on beliefs rather than observations, and it does not infer its principles from observations.